For a User Equipment (UE), the 3rd Generation Partnership Project (3GPP) defines only a Closed Subscriber Group (CSG) list in the Release 8 (R8), which is referred to as an Allowed CSG list or simply an ACL in this context.
An Operator CSG List (simply an OCL in this context) is introduced in the Release 9 (R9). An OCL may also be referred to as an Operator Controlled CSG List (OACL) in the R9.
For an allowed CSG list in the R8, a further need arises during a study of the Release 9 to allow a user to modify the ACL, and this ACL was referred to as a User CSG List (UCL) or a
User Controlled CSG List (UACL) in the earlier specification of the Release 9 and is still referred to as an ACL in the latter specification of the R9 and the releases subsequent to the R9.
CSG subscription data, instead of the ACL and the OCL, is stored at the network side. CSG subscription data of a UE is stored in a Home Subscriber Server (HSS), a Mobility Management Entity (MME), a Serving GPRS Support Node (SGSN), a Mobile Switching Center (MSC) and other network nodes, which perform access control on the UE according to the CSG subscription data.
There is a further logic entity in the network, which is referred to as a CSG list server and updates the ACL and the OCL at the UE side in an Over-The-Air (OTA) or Open Mobile Alliance OMA DM Device Management (OMA DM) methods. This update method is characterized in updating the entire ACL or OCL of the UE.
In addition to the OTA and OMA DM methods, there is a further manual updating method (that is, in a Non Access Stratum (NAS) procedure) to update the ACL and the OCL at the UE. An underlying principle of the manual updating method lies in that the UE performs an NAS procedure in a specific CSG cell, and if the NAS procedure is accepted by the network, then a CSG ID of the CSG cell is added into the ACL (if the CSG ID is absent in the ACL), or if the network rejects the NAS procedure and gives a rejection reason of #25, then the CSG ID is deleted from the ACL (if the CSG ID is present in the ACL). The manual updating method (a method in an NAS procedure) can only update an ACL and can be performed only when the UE performs an NAS procedure in a CSG cell; and this method can not update the entire ACL concurrently.
In the UE, the NAS is responsible for maintaining and updating the OCL and the ACL and hereby generating a White CSG List (simply a WCL in this context) for use by an Access Stratum (AS). The AS selects a cell, prepares for a handover and other procedures according to the WCL.
The network may be configured not to use any ACL according to an operator policy.
As stated in the section of Closed Subscriber Group, the 3GPP Specification TS 22.220 5.3.2 for a demand of a CSG, the two lists, i.e., the ACL and the OCL, are maintained independently from each other. A change in the Operator CSG list shall not trigger the UE to modify the Allowed CSG list to reflect such change automatically.
A detailed definition of a method for integrating the ACL and the OCL into the WCL is absent in the existing specification. As current understanding of the specification, the UE regards both of CSGs in the ACL and the ACL as subscribed CSGs. Thus it can be considered that all of CSG IDs in the ACL and the OCL should be list into the WCL (that is, the ACL is combined with the OCL) and provided to the AS as an access control criterion in selecting a cell and in preparing for a handover, etc.
At the UE side, the existing specification considers such a scenario that when the UE performs an NAS procedure (for example, attachment, Tracking Area Update (TAU), Routing Area Update (RAU), and Service Request, etc.) in a specific CSG cell, a rejection reason of #25 is indicated to the UE when the UE is reject for an access to a non-subscribed CSG cell. The UE deletes a CSG ID of the CSG cell from the ACL upon reception of the rejection reason. If the CSG ID is also present in the OCL, then the UE may not include the CSG ID in the WCL under some condition dependent upon an implementation of the UE. Reference can be made to CSG Selection or Restriction, 3GPP 23.122 3.1A for details.
There is a further scenario where if the ACL is updated in the manual update method and the OCL is updated in the OTA or OMA DM method, then such a situation may arise that some CSG IDs are already absent in the OCL but these CSG IDs are still present in the ACL. A reason for this problem is that the network updates the OCL at the UE side through OMA DM or OTA but does not update the ACL as well and instead updates the ACL in an NAS procedure; or the NAS of the UE is going to provide the AS with the WCL before the network updates the ACL. Then the WCL of the UE may include the new OCL and the old ACL, and the NAS provides the AS with the WCL as an access control criterion. In this scenario, the UE selects a cell or performs a handover still according to the contents of the WCL (i.e., the old ACL and the new OCL), and once these CSG IDs are selected, a subsequent procedure will be rejected by the network, thus resulting the problems of degrading a user experience, increasing an unnecessary network signaling overhead, etc.
A drawback of the prior art lies in the absence of a technical solution to the foregoing two scenarios occurring.